1. Field of the Invention
This invention relates to electronic component and circuit packaging techniques and, in particular, to packaging techniques useful for the fabrication of dense, high speed digital circuits and subassemblies such as those used in the construction of computers.
2. Description of the Prior Art
The performance of today's computers depend primarily on the performance of the main chip-set subassembly and the cache memory access time of each computer. This performance is limited by the delay of the computer package, including the signal paths interconnecting the integrated circuit chips in the subassembly. These paths include the individual chip packages, the interconnect substrate, the motherboard and the various connectors and cables.
As the operating frequencies of computers approach 100 MHz, packaging delays are increasingly becoming the limiting factor in the operation and performance of today's computers. For these reasons, high performance main frame computers have used various techniques for packaging and assembling the critical chips of a computer in a compact, high frequency unit which is assembled to the next level subassembly, the backplane, with minimal performance loss.
Many packaging techniques have been used for the fabrication of such electronic circuits and subassemblies. The primary requirements for such packaging techniques include high circuit density, convenient construction, testing and repair techniques as well as high speed circuit performance and efficient thermal transfer and dissipation. Many conventional packaging techniques satisfy one or more of these requirements for particular applications.
A currently popular manufacturing technique, known as TAB or Tape Automated Bonding, has proven to be particularly useful for high volume manufacturing of circuit subassemblies. TAB techniques utilize a frame of conductors in a pattern, the inner contacts of each conductor being connected to appropriate contact points on a semiconductor chip. The outer contacts are utilized first for testing purposes and then for permanent bonding connections to the next high level of circuit subassembly, such as a printed circuit board substrate.
A particularly convenient variation of this technique is known as DTAB which stands for Demountable Tape-Automated Bonding and is disclosed in U.S. patent application Ser. No. 07/401,053, filed 08/31/89 and assigned to a common assignee. DTAB utilizes a demountable pressure contact between the outer frame ends and the printed circuit board for electrical connection. An elastomer may be used between the frame contacts and a pressure cap for controlled, demountable electrical connection therebetween.
Heat transfer techniques have become important as circuit densities and speed result in the close proximity of heat generating and heat degradable components. Heat sinks are commonly used to transfer heat from individual components, or groups of substantially identical components, to air or other cooling mediums.
The most commonly used heat transfer techniques position the circuit components active side facing the printed circuit board, and mount a heat sink on the back side. An alternative approach provides a thermal dissipation path through the printed circuit board or other substrate. Such techniques are cumbersome, expensive and substantially interfere with the repairability of individual components.